It is estimated that there are over 100 genes for non-syndromic hearing loss (NSHL). Thus far, 29 genes have been localized for NSHL of which three have been isolated. The goals of this study are: to localize novel NSHL gene(s); establish the geographical distribution of NSHL; refine the genetic region for known NSHL loci; and isolate NSHL genes. NSHL kindreds are being ascertained which can independently establish linkage to localize novel NSHL loci as well as smaller kindreds which can facilitate fine mapping of NSHL loci. Localizing genes responsible for NSHL is challenging due to extreme genetic heterogeneity. The genetic regions for NSHL loci are often imprecise, due to the limited number of families available for study for each locus. Therefore mutation detection in candidate genes will be used to isolate NSHL genes. A gene will be considered a candidate if it meets the following criteria: maps to the physical region of a NSHL locus; and has tissue specific expression (i.e. cochlea). Candidate genes will be sequenced in controls and affected individuals from families with a high probability of segregating the NSHL loci of interest. The importance of obtaining good clinical data is stressed in order to develop phenotype/genotype relationships.